Catalyst components for the polymerization of olefins, obtained by reacting MgCl2.nEtOH adducts with halogenated transition metal compounds, are described in U.S. Pat. No. 4,399,054. The adducts are prepared by emulsifying the molten adduct in an immiscible dispersing medium and quenching the emulsion in a cooling fluid to collect the adduct in the form of spherical particles. The number of moles of alcohol per mole of MgCl2 is generally 3. In order to increase the morphological stability and render the catalyst suitable to produce more porous polymer particles, capable in itself to be used in the preparation of sticky polymers, the alcohol content of the adduct is lowered, before reaction with the titanium compound, to values in the range of 2-2.5 moles. As a positive result, the porosity of the catalyst is increased, but as a downside, the catalyst activity becomes too low.
In WO2004/026920 it is proposed to prepare adducts having an increased amount of alcohol and characterized by a particular X-ray diffraction spectrum. These adducts, if converted as such into catalyst component are able to generate catalysts with increased activity. On the other hand, if the adducts are partially dealcoholated before reaction with the Ti compound, provide a catalyst with a higher porosity content. However, the catalysts obtained by these adducts show a unsatisfactory balance activity and stereospecificity in the polymerization of propylene.
The applicant has now found new MgCl2.mEtOH adducts having specific chemical and physical properties. The adducts of the present invention are characterized by enhanced porosity with respect to the adducts of the prior art having the same alcohol content. The adducts of the present invention can be used to prepare catalyst components for the polymerization of olefins by reacting them with transition metal compounds.